Spinal interspace shaper

ABSTRACT

A device and method for use in a vertebral spine to prepare a space between adjacent vertebral bodies to receive an implant. The device includes a shaft, and a mounting member at one end of the shaft. A working end is mounted on the mounting member and is coupled to a drive mechanism adjacent to the working end. The drive mechanism is operable to move the upper and lower cutters of the working end to create surfaces having predetermined contours in the end plate region of the adjacent vertebral bodies. A guard provides protected access to the disc space and the adjacent vertebral bodies for the working end of the bone removal device through a passageway.

RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/972,560, which claims benefit of Provisional Application No.60/255,463, filed Dec. 14, 2000; all of which are incorporated byreference herein.

BACKGROUND

[0002] Present methods of forming an implantation space between adjacentvertebral bodies in the human spine generally include the use of one ormore of the following: hand held biting and grasping instruments knownas rongeurs; curettes; drills and drill guides; rotating burrs driven bya motor; and osteotomes and chisels. Sometimes the vertebral end platemust be sacrificed as occurs when a drill is used to drill across thedisc space and deeper into the vertebral bodies than the thickness ofthe bony end plate region. Such a surgical procedure necessarily resultsin the loss of the hardest and strongest bone tissue of the vertebralbodies located in the bony end plate region and thereby removes from thevertebral bodies that portion of its structure best suited to absorbingand supporting the loads placed on those vertebral bodies by aninterbody spinal implant. Nevertheless, the surgeon must work upon theadjacent end plates of the adjacent vertebral bodies to access theunderlying vascular bone that is capable of participating in the fusionby allowing active bone growth, and also to attempt to obtain anappropriately shaped surface in the vertebral bodies to receive theimplant. Because the end plates of the adjacent vertebral bodies are notflat, but rather have a compound curved shape, and because the implants,whether made of bone or any other suitable implant material, whenfabricated or manufactured, tend to have a geometric rather than abiologic shape, it is generally necessary to conform at least a portionof the vertebral bodies to the shape of the implant to be receivedtherebetween.

[0003] It is important in forming the space between the adjacent bonestructures to provide a surface contour that closely matches the contourof the implants so as to provide an adequate support surface acrosswhich the load transfer between the adjacent bone structures can beevenly applied. In instances where the surgeon has not been able to formthe appropriately shaped space for receiving the implants, thoseimplants may slip or be forcefully ejected from the space between theadjacent vertebral bodies, or lacking broad contact between the implantand the vertebral bodies, a failure to obtain fusion may occur.

[0004] Prior devices having a plurality of rotating cutting elements forremoving bone with a drive mechanism between the cutting elements hadlimitations in certain applications. For example, if the bone to be cutwas thicker than the individual thickness of each of the cuttingelements, then the portion of the device between the cutting elementscould hit the uncut bone and stop the bone removal device from advancingdeeper into the bone being cut. Further, the presence of the drivemember between the cutting elements kept the cutting elements spacedapart and thus could prevent the placement of the bone removal deviceinto very narrow spaces such as, but not limited to, disc spaces asmight be found in some instances in the cervical spine.

[0005] There remains therefore a need for an improved spinal interspaceshaper that does not have such limitations so as to achieve the desiredpurposes as described herein.

SUMMARY OF THE INVENTION

[0006] The present invention relates to a bone removal device forinsertion into and at least in part across the height of a disc spacebetween adjacent vertebral bodies in the human spine, and a guard forproviding protected access to the disc space and for maintaining adesired positioning of the adjacent vertebral bodies relative to eachother, and to a method of working on those portions of the vertebralbodies adjacent that disc space to remove bone material sufficient toform a desired contoured end plate and to thereby access the underlyingvascular bone. For purposes of this application, the bony “end plateregion” of the vertebral bodies is defined as the outer shell of compactbone (the bony end plate) adjacent to the spinal disc and the underlyingsubchondral zone.

[0007] The apparatus and associated method of the present invention isadapted to form a surface on or into each of the vertebral body surfacesthat are adjacent the intervertebral disc space. The prepared spaces areformed through the inert outer bone of the vertebral bodies to get tothe vascularized underlying bone, preferably, without generally removingall of the thickness of the end plate region. The formed surface(s) havea defined shape and a contour corresponding to a preferred interbodyspinal implant to be implanted in the disc space.

[0008] The bone removal device of the present invention is useful in thecervical, thoracic, and lumbar spine from anterior to the transverseprocesses of the vertebrae, lateral or anterolateral in the thoracic andlumbar spines, or from posterior in the lumbar spine. The bone removaldevice, in a preferred embodiment, generally includes a cutting elementmovably and preferably replaceably mounted on the distal end of a shaft.A depth limiting mechanism preferably controls the depth of insertion ofthe cutting element into the intervertebral space (i.e., the discspace). The device also includes a handle that may be detachable fromthe shaft. As used herein, the term “handle” refers to a portion of thedevice that a surgeon may grip or otherwise manipulate to guide theworking end of the device. That “handle” may in fact have multiplepurposes. For example, the handle may be a portion of the shaft on whichthe working end is mounted at one end. Alternatively, the handle may bepart of a segment that connects the device to a power source. Forexample, the handle may be part of a power source that suppliespressurized gas to the power source if turbine driven, or the handle maybe a drill, but the term “handle” is used herein in its broadest contextto refer to that which the surgeon grasps to use the present invention.

[0009] Additionally, the shaft may be detachable from the working end.The device also includes a drive mechanism that transmits power toactivate, i.e., move, the cutters. The drive mechanism connects to anenergy source, e.g., a rechargeable battery that further may be but neednot be housed within the handle of the device. By way of example only,the drive mechanism may include an electric motor or an electromagneticoscillating mechanism. Or, again by way of example only, the drivemechanism and handle in which it may be disposed may include the headunit of a gas powered turbine of a type commonly used in other surgicalinstruments.

[0010] In a preferred embodiment, the working end is generally as wideas the spinal implant to be implanted or the width of a combinedplurality of implants adapted for side-by-side use between the adjacentvertebral bodies adjacent the disc space. The receiving bed, i.e., theprepared surface of the vertebral bodies, when formed by the device,will correspond in shape, size, and contour to the correspondingsurfaces of a preferred spinal implant or combined width of implants tobe implanted. The surface produced by the bone removal device isgenerally flat or concave to correspond to the upper or lower vertebralbody contacting surfaces of the implant that will be implanted betweenthe vertebral bodies. In an embodiment of the present invention havingdomed or convex upper and lower cutters or cutting members the devicemay be inserted into the spine and then turned on to form to desiredshape into the adjacent vertebral bodies. The cutters have a leading endthat is capable of cutting through bone and/or disc material to form apocket or socket having a contour corresponding to the forward aspect ofthe leading end, as well as at least a portion of the side surfaces ofthe preferred implant to be implanted. These sidewalls assist inrestraining the implant from lateral movement.

[0011] The working end of the present invention includes a pair ofopposed, outwardly facing cutters which lie in planes that may be eitherparallel to each other or, alternatively, convergent to each other. Thepresent invention saves time by simultaneously preparing both of thevertebral end plates adjacent a disc space. The bone removal deviceshapes the three-dimensional space created between the adjacentvertebral bodies, which space can be made to conform to the desiredlordosis of that portion of the spine that will receive the implant. Theend plate space may be, but need not be, identical to the height of theimplant, as the implant may be there to optimize the distance of thedisc space.

[0012] The drive mechanism of the bone removal device is preferablylocated adjacent the working end of the instrument permitting areduction in the overall height of the cutting elements. Thisconfiguration permits the overall height of the cutting mechanism to bethicker or given the same height, it can be less than what waspreviously possible with the cutting elements having a drive membertherebetween because the cutting elements can be placed closer together.A reduced overall height of the cutting mechanism permits the placementof the bone removal device into narrower spaces, such as but not limitedto disc spaces as might be found in some instances in the cervicalspine, than previously possible. Moreover, because the space between thecutting elements is minimized, the thickness of the cutting elements maybe increased.

[0013] The cutting element of the present invention is not limited tobeing a unitary, one-piece construction, regardless of the number ofcutting surfaces of the cutting element. The cutting element may includemultiple pieces that, by way of example and not limitation, aremountable on the end of the device to, in combination, define theoverall shape of the cutting element and its surfaces. Thus, the term“cutting element” is used herein to refer to both a unitary, one-piececonstruction or a multi-piece construction.

[0014] The cutting element is preferably mounted on the mounting memberand may be removable and interchangeable. In such an embodiment, themounting member may be, but does not have to be, attachable to a shaftthat is attachable to the handle. cutting element and the mountingmember may be separable from each other. Alternatively, the working endand the mounting member may, together, be removable from the handle.

[0015] While a preferred embodiment of the present invention isdiscussed and disclosed herein for creating a space between adjacentvertebral bodies in the spine, the present invention is not limited to adevice for creating a space between adjacent vertebral bodies, but canalso be used in other portions of the body where it is desirable toplace an implant between adjacent bone structures. Furthermore, anembodiment of the present invention may have upper and lower cuttingsurfaces that are in angular relationship to each other so as to, forexample, match the natural lordotic curvature of the human spine at thelocation of the vertebral bodies to be operated upon. Additionally,sequentially larger, that is wider and/or thicker, ones of the cuttingelements, or mounting member, may be used to form the desired sizedspace in a step-wise fashion, or the working end may be sized tosubstantially match the final desired width of the surface to be formedin the vertebral end plate. Furthermore, the working end is preferablyconfigured with a sharpened leading edge to allow the working end to“forward cut” as it is inserted between the adjacent vertebral bodies.In this manner, progressive insertion of the cutting element between thevertebral bodies is facilitated.

[0016] In a preferred embodiment, a guard for use with the bone removaldevice has a body with a passageway passing therethrough. In a preferredembodiment, a first disc penetrating extension and a second discpenetrating extension extend from the leading end of the guard and areadapted to be inserted into the disc space between adjacent vertebralbodies. The disc penetrating extensions are preferably adapted todistract and align the disc space, and restore lordosis. The discpenetrating extensions also further limit lateral excursion of the boneremoval device and protect vital structures lateral to the disc space.In the alternative, the guard could be attached with screws or pins toeach of the vertebral bodies like portions to bear upon the end plates.

[0017] The guard provides protected access to the disc space and theadjacent vertebral bodies for the working end of the bone removal devicethrough a passageway, which may be sufficiently taller than the heightof the space to be formed by the working end so as to allow for thesequential use of working ends of increasing height or the insertion ofa spinal implant taller than the height of the working end therebyallowing the surgeon the option of keeping the guard in place after thecutting procedure. For example, the guard can be left in placedistracting and aligning the adjacent vertebral bodies after the cuttingstep so that spacers (i.e. trial implants) can be trialed and then theimplant of the optimal height, and perhaps of a greater height than thecutter, can be inserted.

[0018] The bone removal device preferably remains appropriatelypositioned relative to the height of the passageway during the cut. Byway of example and not limitation, this may be achieved by having thebone removal device and guard aligned by a cooperative track, or alongitudinal groove and cooperating protrusion. In an alternativeembodiment, a mounting element may be located between the cuttingportion at the leading end of the bone removal device and the trailingend of the bone removal device. In a preferred embodiment, the mountingelement can be taller than the cutting portion. When the taller mountingelement passes through the passageway of the guard, it contacts theinterior of the passageway to maintain the cutting portion in apreferred orientation to the guard so that the cutting portion can forman implantation space of a height less than the height of the passagewaythat is still properly positioned relative to removing the densethickness of bone from each of the vertebral bodies adjacent the discspace being prepared. This height differential permits an implant havinga height greater than the height of the implantation space to beinserted through the guard. Somewhere along the shaft an enlargedportion may cooperate with the inner height and even the rearwardportion of a guard.

[0019] The leading end of the guard may have a foot plate adapted tocontact the vertebral bodies when for use generally anteriorly oranteriorlaterally and may be contoured to generally conform to at leasta portion of the exterior aspect of the vertebral bodies wherecontacted. The foot plate may have holes for receiving, for example,fasteners including spikes, bone screws, pins, prongs, nails, or theequivalent therethrough to secure the foot plate to the vertebral bodiesor such spikes, bone screws, pins, prongs, or nails maybe part of thefoot plate. The attachment of the guard with fasteners to the adjacentvertebral bodies may further secure the vertebral bodies in the desiredrelationship and hold the vertebral bodies steady for the cuttingoperation to be performed.

[0020] For use posteriorly, it is generally preferred that the guardhave at least one and more preferably two disc penetrating extensions,such that a foot plate may be minimized or absent.

[0021] Thus, the present invention provides a device and method forpreparing a disc space between adjacent vertebral bodies to receive aspinal implant, and prepares that disc space by removing a portion ofthe bony end plate region of those vertebrae adjacent that disc space toform predetermined surfaces in that vertebral bodies adjacent the discspace. The prepared spaces are formed through the inert outer bone ofthe vertebral bodies to get to the vascularized underlying bone,preferably, generally without removing the full thickness of bone in theend plate region. The prepared surfaces are sized and contoured to havebroad intimate contact with the preferred spinal implant to be implantedbetween the adjacent vertebral bodies and along side walls of a socket,which broad contact provides for increased implant stability. This broadarea of intimate contact between the vertebral bodies and the implantpromotes bone ingrowth from the vertebral bodies into the implant, andalso provides a broad area over which to support the incumbent loads soas to minimize the risk of vertebral collapse or subsidence of theimplant into the vertebra.

[0022] While the present invention has been generally described above,and the preferred embodiments of that invention will be described indetail below, neither that general description nor the detaileddescription limits the scope of the present invention. That scope isdefined by the claims appearing at the end of this patent specification.

OBJECTS OF THE PRESENT INVENTION

[0023] It is an object of certain embodiments of the present inventionto provide a device and method for quickly, safely, effectively, andaccurately working upon the region of the bony vertebral body end plateregions adjacent a disc space so as to, while preferably preserving boneof that region, to at least in part, remove bone such that to access theactive bone growth end plate at least in part, remove bone to produce asocket to accept and implant corresponding in size, shape, and contourto an implant to be implanted between the adjacent vertebral bodies.

[0024] It is a further object of certain embodiments of the presentinvention, to provide a device capable of simultaneously working uponboth of the vertebral body end plate regions adjacent a disc space toproduce opposed receiving surfaces in the adjacent end plate regionscorresponding in size, shape and contour to a preferred implant to beimplanted, and in so doing to define the shape of the implant space.

[0025] It is a further object of certain embodiments of the presentinvention to provide a vertebral interspace preparation device that, ina preferred embodiment, is capable of working with linear insertion,i.e., insertion along a single axis, and without the need tosubstantially move the device from side to side within the disc spacealong a second axis. In such a preferred embodiment, the device has at aworking end having a width generally corresponding to the width of theimplant to be implanted, and a leading edge corresponding to a generallyarcuate leading end of the implant to be implanted, for creating a spaceof a fixed geometry corresponding to an implant of correspondingdimensions.

[0026] It is a further object of certain embodiments of the presentinvention to have a safety mechanism built into the device that limitsthe depth of insertion of the device into the spine.

[0027] It is a further object of certain embodiments of the presentinvention to provide a vertebral interspace preparation device that canhave interchangeable working ends so as to be capable of producing avariety of differently sized and contoured surfaces and shapes withinthe intervertebral space.

[0028] It is a further object of certain embodiments of the presentinvention to have cutters extending to the leading end of the devicesuch that the device may remove bone along its leading end as it isadvanced within the disc space.

[0029] These and other objectives of the present invention will occur tothose of ordinary skill in the art based on the description of thepreferred embodiments of the present invention described below. However,not all embodiments of the inventive features of the present inventionneed achieve all the objectives identified above, and the invention inits broadest aspects is not limited to the preferred embodimentsdescribed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1A is a front elevation view of two disc levels of the lumbarspine showing the prior art depth of resection resulting from drillingcompletely through the bony end plate region of adjacent vertebralbodies and showing the end plate region on a vertebral body;

[0031]FIG. 1B is a top plan view of a spinal interspace shaper boneremoval device in accordance with one embodiment of the presentinvention;

[0032]FIG. 2 is a side elevation view of the bone removal device of FIG.1B;

[0033]FIG. 3 is an enlarged fragmentary view along line 3 of FIG. 2;

[0034]FIG. 4 is a detailed fragmentary view of the cutting portion anddrive gears of the spinal interspace shaper bone removal device of FIG.1B;

[0035]FIG. 5 is a trailing end view of an extended guard in accordancewith one embodiment of the present invention;

[0036]FIG. 6 is a top plan view of the extended guard of FIG. 5;

[0037]FIG. 7 is a side elevation view of the extended guard of FIG. 5;

[0038]FIG. 8 is an exploded view of the bone removal device of FIG. 1B,extended guard, and installation screws in accordance with oneembodiment of the present invention;

[0039]FIG. 9 is a side elevation view of a human spine with theinstrumentation of FIG. 8 being used from an anterior approach to thespine;

[0040]FIG. 10 is a side elevation view of the extended guard beinginstalled from an anterior approach into the disc space between twoadjacent vertebral bodies and being secured thereto by screws;

[0041]FIG. 11 is a partial side sectional view of two adjacent vertebralbodies with the extended guard in partial cross-section installed intothe disc space and secured to the adjacent vertebral bodies byinstallation screws with a bone removal device about to be insertedtherein;

[0042]FIG. 12 is a trailing end view of the extended guard of FIG. 11installed into the disc space and secured to the adjacent vertebralbodies by installation screws;

[0043]FIG. 13 is a partial side sectional view of two adjacent vertebralbodies with the extended guard of FIG. 11 in partial cross-sectioninstalled into the disc space and secured to the adjacent vertebralbodies by installation screws with a bone removal device insertedtherein and into the disc space;

[0044]FIG. 14 is a partial side sectional view of two adjacent vertebralbodies with the extended guard in partial section installed into thedisc space and secured to the adjacent vertebral bodies by installationscrews with the installation space formed across the disc space and intothe adjacent vertebral bodies;

[0045]FIG. 15 is a partial side sectional view of two adjacent vertebralbodies with the extended guard of FIG. 11 being removed;

[0046]FIG. 16 is a top plan view of an end plate of a lumbar vertebralbody with an implantation space formed therein from an anterior approachwith the instrumentation and method in accordance with the presentinvention;

[0047]FIG. 17 is a top plan view of an end plate of a cervical vertebralbody with an implantation space formed therein from an anterior approachwith the instrumentation and method in accordance with the presentinvention; and

[0048]FIG. 18 is a top plan view of an end plate of a lumbar vertebralbody with implantation spaces formed therein from a posterior approachwith the instrumentation and method in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0049] The following description is intended to be representative onlyand not limiting. Many variations can be anticipated according to theseteachings, which are included within the scope of the present invention.Reference will now be made in detail to a preferred embodiment of thisinvention, an example of which is illustrated in the accompanyingdrawings.

[0050] Human vertebral bodies have a hard outer shell of compacted densecancellous bone (sometimes referred to as the cortex) and a relativelysofter, inner mass of cancellous bone. Just below the cortex adjacentthe disc is a region of bone referred to herein as the “subchondralzone”. As best shown in FIG. 1A, the outer shell of compact bone (thebony end plate) adjacent to the spinal disc and cartilaginous end plateand the underlying subchondral zone are together herein referred to asthe bony “end plate region” and, for the purposes of this application,is hereby so defined. In the lumbar spine the thickness of the cortexend plate adjacent the disc space is generally not greater than severalmillimeters deep. By way of example, prior art threaded implantsrequiring approximately a 3 mm drill depth into the vertebral body andhaving threads of approximately 1 mm or more in height result in a totaldepth of penetration into the vertebral body of at least 4 mmsacrificing the best structural bone adjacent the disc space. Thepresent instrumentation and method permits the preparation of the interspace to receive an implant with less depth of penetration into thevertebral bodies.

[0051] FIGS. 1B-4 show various views of bone removal device 100 inaccordance with a preferred embodiment of the present invention. FIG. 1Bis a top view of bone removal device 100 and FIG. 2 is a side viewthereof. Bone removal device 100 has a leading end 102 including acutting mechanism 104, and an opposite trailing end 106 configured tocooperatively engage a driving mechanism, such as a power drill,turbine, and the like, or an electrical driving mechanism suitable forthe intended purpose. The particular power source that powers boneremoval device 100 does not form a part of the present invention exceptto the extent it is adapted to achieve the appropriate and desirableamount of movement of the working end, or serves as part of the “handle”when in use.

[0052] As shown in FIGS. 1B and 4, cutting mechanism 104 includes adrive element 108 and a working end 110. Working end 110 preferablyincludes two opposed cutters, upper cutter 112 and lower cutter 114 thatare configured with a sharpened leading edge. In this embodiment,working end 110 preferably includes two disc-shaped cutting members 116,118 that are removably mounted on the distal end of the device by arecessed connector 120 and connector shaft 122. Upper cutter 112 isformed on the edge of cutting member 116, and lower cutter 114 is formedon the edge of cutting member 118. Mounting member 152 facilitatesremoving cutting members 116, 118 and replacement with other disc-shapedmembers of similar or alternative cutting or abrading designs. Brace 124prevents rotation of shaft 126 during use of the device such as bychucking shaft 26 into a drill and fitting brace 124 into a non-rotatingportion of the drill.

[0053] In an alternative embodiment, cutters 112, 114 may bemanufactured separately from cutting members 116, 118. For example, inFIG. 4, disposable or interchangable ring 128 includes upper cutter 112and disposable or interchangable ring 130 includes lower cutter 114.Cutting ring 128 is mounted on cutting member 116, and cutting ring 130is mounted on cutting member 118. Such a mounting may be accomplished bythreadably connecting a cutting ring to its associated cutting member.The threads of such a threadable connection preferably oppose thedirection of rotation of the cutting member when the device is in use.Other equivalent mountings to the threadable connection may be employed,such as where the ends of the wheel are configured such that one endsecures into the other.

[0054] Drive element 108 is positioned to rotationally engage workingend 110. Drive element 108 is preferably located adjacent to cuttingmembers 116, 118. Drive element 108 preferably includes two disc-shapeddrive members 132, 134 (shown in phantom in FIG. 4). Drive members 132,134 may be removably mounted on bone removal device 100 by a connector136 and connector shaft 138. Although two disc-shaped elements arepreferred, it should be understood that a number of equivalentstructures may be used to impart rotation to working end 110. Forexample, instead of two drive members 132, 134 as shown in FIG. 4, ahollow or solid cogwheel could be used to interface between working end110 and a driving mechanism. Another alternative could employ the use ofa threaded spindle acting as a drive element. Alternatively, a pulley,spindle, or other rotating device may be coupled to a power source todrive a cord, cable, or belt, or similar power-transferring element tothereby drive cutters 112, 114. Such an alternative embodiment removesthe bulk of the drive mechanism from between cutters 112, 114 and iswithin the scope of the present invention. It is also possible andwithin the scope of the present invention to angle the cutting elementssuch that they converge towards leading end 102 to form an angled cutinto the adjacent vertebral bodies.

[0055] Upper and lower cutting members 116, 118 and their associatedcutters may rotate in opposite directions so as to mitigate anyundesired torque and to avoid any tendency of the cutting end of thedevice to move laterally. This counter-rotating motion may be achievedby using a rotating drive rod 140 that extends through shaft 126 and isconfigured with a gear 142 at its distal end that engages with matinggear teeth 144, 146 formed on respective sides of drive members 132,134. The resulting counter-rotation of drive members 132, 134 (shown byarrows A in FIG. 4) acts to counter rotate cutting members 116, 118 byway of cutting member engagement surfaces 148, 150, shown in FIG. 4 asradial teeth. This counter-rotating motion of members 116, 118 isillustrated by the arrows B in FIG. 4. Mating gear teeth 144, 146 may beinwardly sloping, ramped surfaces that engage cone-shaped gear 142disposed on the distal end of a rotating drive rod 140 to turn drivemembers 132, 134 in opposite directions as drive rod 140 spins about itsaxis. Alternatively, cutting member engagement surfaces 148, 150, anddriver 140 can be radially splined to engage one another or may compriseof any other known cord, cable, belt or similar power transferringelement that operatively drives cutters 112, 114.

[0056] In the embodiment described, mounting element 152 mayinterchangeably receive various sizes of working end 110 and/or drivingelement 108. Thus, element 108 and/or working end 110 may be quickly andeasily attached to and detached from mounting member 152 during surgery.In order to accommodate the various sizes of working ends and drivingelements, mounting member 152 may be adapted to permit slidableadjustment between shafts 122 and 138. While in a preferred embodiment,upper and lower cutters 112, 114 are selected to have a width that issubstantially the same as the width of the surface to be formed in thevertebral end plate, a surgeon might also elect to use a working end oflesser height than the ultimate desired depth of the surfaces to beformed. Thereafter, the surgeon may use a successively wider and/ortaller work ends of the bone removal device until he arrives at thedesired dimensions of the space formed between the adjacent bonestructures.

[0057] The positioning of drive members 132, 134 adjacent to cuttingmembers 116, 118, instead of between cutting members 116, 118, permitsthe overall thickness of cutting mechanism 104 to be less than waspreviously possible with cutting members 116, 118 having the bulk of adrive member therebetween because cutting members 116, 118 can be placedcloser together. A reduced overall thickness of cutting mechanism 104permits the placement of bone removal device 100 into narrower spaces,such as in narrow disc spaces for example, such as but not limited todisc spaces as might be found in some instances in the cervical spine,than was previously possible. Moreover, because the space betweencutting members 116, 118 is reduced, the thickness of the cutting areamay be increased to permit cutting thicker pieces of bone. For example,in prior devices where a relatively thick portion of the drive mechanismis located between the cutting members, if the bone to be cut is thickerthan the individual thickness of each of the cutting members, then theportion of the device between the cutting members could hit the uncutbone and stop the bone removal device from advancing deeper into thebone being cut.

[0058] As shown in FIG. 3, in a preferred embodiment a thin portion 154of mounting element 152 extends between cutting members 116, 118 toprovide support and permit attachment of cutting members 116, 118 tomounting element 152. As shown in FIG. 2, a depth stop 156 having an end159 for abutting a substrate to be cut, such as for example the exteriorof a vertebral body, is in slideable engagement to mounting element 152so as to adjust the depth of penetration of cutting mechanism 104 ofbone removal device 100. An adjusting mechanism 158, such as aspring-biased lever for example, locks depth stop 156 at the depthselected by the surgeon. Depth stop 156 also may include an abutmentsurface or any number or shape of projection capable of carrying out theintended function and any known means for securing it. Adjustmentmechanism 158 may also comprise a number of equivalent structures, suchas, for example, one or more push button spring locks, adjustable turnscrews, a collar with spring loaded detents or ball bearings and thelike. Brace 124 extends from trailing end 106 for holding bone removaldevice 100 in a desired position relative to the drive means to which itattaches.

[0059] In another embodiment, mounting element 152 can be taller thancutting members 116, 118. When the taller mounting element 152 passesthrough the passageway of guard 160, it contacts the interior of thepassageway to maintain the cutting mechanism 104 in a preferredorientation to guard 160 so that cutting mechanism 104 can form animplantation space of a height less than the height of the passageway.This height differential permits an implant having a height greater thanthe height of the implantation space to be inserted through guard 160.

[0060] As a further enhancement to the device it may have evacuationflutes for moving debris proximal. Additionally, an irrigation tubeand/or a suction tube may be formed within, or outside of shaft 126.These irrigation and suction tubes may be connected to appropriatesources of irrigation fluid and a source of vacuum, respectively, toefficiently irrigate and clear the surgical site during use of thedevice.

[0061] Numerous other configurations of working end 110 are possiblewithin the scope of the present invention. For example, upper and lowercutters 112, 114 may be convex to form concave receiving surfaces in thevertebral end plates. The geometry and configuration of the shapes ofthe upper and lower cutters and cutting members can be matched to thedesired shape and configuration of the space which the surgeon intendsto create between adjacent bone structures and to the desired contour ofthe surfaces created in the bone structures as is disclosed inapplicant's International Patent Application No. PCT/US99/12890, filedJun. 9, 1999, and applicant's U.S. Pat. No. 6,083,228, issued Jul, 4,2000, both of which are incorporated herein by reference.

[0062] Additionally, working end 110 may be configured to haveroughenings, knurls, ridges, small pyramid shaped projections, or anyother surface configuration that is capable of cutting or abrading thebone structures.

[0063] FIGS. 5-7 show a guard 160 for use with device 100. In thepreferred embodiment, guard 160 has a body 166 with a leading end 162, atrailing end 164 opposite leading end 162, and a passageway 168 passingtherethrough. In a preferred embodiment, a first disc penetratingextension 170 and a second disc penetrating extension 172 extend fromleading end 162. First disc penetrating extension 170 and second discpenetrating extension 172 are adapted to be inserted into the disc spacebetween adjacent vertebral bodies. Guard 160 provides protected accessto the disc space and the adjacent vertebral bodies for working end 110through opening 168. Opening 168 is preferably taller than the height ofworking end 110. Such a taller opening 168 allows the sequential use ofworking ends 110 of increasing thickness or the insertion of a spinalimplant taller than the thickness of working end 110 thereby allowingthe surgeon the option of keeping guard 160 in place after the cuttingoperation. Additionally, body 166 may have a cross section transverse toits longitudinal axis with a complete or incomplete perimeter, (i.e. thecross section may be generally square, rectangular, oval, circular orany other shape with either an open or closed perimeter suitable for theintended purpose). The spinal implant is preferably sized and shaped tomatch the space formed in the spine by the working end.

[0064] Leading end 162 of guard 160 preferably has a foot plate 174 (foruse anteriorly) adapted to contact the vertebral bodies and may becontoured to generally conform to at least a portion of the exterioraspect of the vertebral bodies in any or all planes. Foot plate 174preferably is adapted to cover at least a portion of each of the twovertebral bodies adjacent the disc space into which guard 160 is to beinserted. Foot plate 174 may have receiving holes 176, 178 forreceiving, for example, fasteners including spikes, bone screws 196,198, pins, prongs, nails, or the equivalent therethrough to secure footplate 174 to the vertebral bodies. The attachment of foot plate 174 withscrews 196, 198 or the equivalent to the adjacent vertebral bodies mayrigidly secure the vertebral bodies in the desired relationship and holdthe vertebral bodies steady for the cutting operation to be performed,when the guard does not have disc penetrating extensions, or furthersecure it when it does. The disc penetrating extensions may be entirelysufficient by themselves such that no other means for securing the guardis needed. The example of the foot plate shown in FIGS. 5-8 is suitablefor use in the anterior cervical spine. For use in the lumbar spine,preferably little or no foot plate would extend outward from the body ofthe guard, as the body of the guard itself functions as a depth limitingstop.

[0065] Guard 160 also may include one or more guide surfaces along theinterior surface of passageway 168 to direct cutting mechanism 104 whileaccessing the disc space and adjacent vertebral bodies throughpassageway 168. Such guide surfaces may include any structure designedto direct the cutting mechanism. For example only, such structures caninclude a cooperative track, longitudinal groove, cooperatingprotrusion, and the like. However, it is emphasized that the guidesurface may include any surface designed to direct cutting mechanism104.

[0066] As shown in FIG. 8, first disc penetrating extension 170 andsecond disc penetrating extension 172 have an upper surface 180 and alower surface 182 adapted to contact and support the end plates of theadjacent vertebral bodies. Upper and lower surfaces 180, 182 can begenerally parallel to each other or can be in angular relationship toeach other. One or both of upper and lower surfaces 180, 182 may betapered proximate their insertion end to facilitate insertion ofextensions 170, 172 into the disc space. An example of a configurationof extensions 170, 172 for use in the cervical spine that generallyconforms to the bony architecture within the disc space is best shown inFIGS. 7 and 11. In the lumbar spine, for use from the posteriorapproach, extensions 170, 172 may have any configuration useful for theintended purpose including but not limited to those disclosed inapplicant's U.S. Pat. No. 6,080,155 filed Feb. 27, 1995, incorporatedherein by reference.

[0067] While not requisite, extensions 170, 172 are preferably adaptedto distract and align the disc space, and to restore lordosis.Extensions 170, 172 further limit lateral excursion of bone removaldevice 100 and protect vital structures lateral to the disc space.Trailing end 164 of guard 160 cooperates with depth stop 156 of boneremoval device 100 to limit the depth of penetration of cuttingmechanism 104 into the disc space. Guard 160 assures balanced resectiondepth of each of the adjacent vertebral bodies and restrains migrationof debris generated by the bone removal device. As best shown in FIG.12, after guard 160 is properly positioned relative to the adjacentvertebral bodies, guard 160 provides the surgeon a line of sight throughpassageway 168 to evaluate the bone resection prior to actuallyperforming it. As the length of the extensions 170, 172 are known to thesurgeon and are appropriate for their intended purpose, the surgeon can,by direct observation, measurement, and/or x-ray, assess the appropriatedepth for resection and implantation. Other shapes of disc penetratingextensions may be desired and are within the scope of the presentinvention.

[0068] Having described the apparatus, methods for its use will now bedescribed. It should be understood that the order disclosed is onlypreferred and that the steps may be performed in other orders whilestill being within the scope of the present invention. Additionally,some steps may be repeated or omitted as necessary.

[0069] Referring to FIGS. 9-15, a method for use in the cervical spinefrom the anterior approach is described by way of example. As shown inFIG. 9, the correct disc space to be operated upon is identified by thesurgeon by direct vision and counting, or preferably, by the useradiographical imaging with a marker. After the correct disc isidentified, guard 160 is inserted into the disc space between theadjacent vertebral bodies as shown in FIG. 10.

[0070] The disc may have a portion excised and then guard member 160 isinserted such that extensions 170, 172 penetrate the disc space andcontact the adjacent vertebral end plates adjacent that disc space.Guard insertion may be performed over a long distractor such asdisclosed in applicant's U.S. Pat. No. 6,159,214, incorporated herein byreference. It is appreciated that guard 160 may be inserted into thedisc space where the spinal disc is still in place; where at least aportion of the disc has been removed and a distractor is inserted intothe disc space and guard 160 is placed over the distractor; or the guardmay be inserted into the disc space without first using a distractor.

[0071] As shown in FIG. 10, extensions 170, 172 of guard 160 are shapedto penetrate the disc space to help secure guard 160 in position to thespine. Extensions 170, 172 may also be beneficial in spacing apart thevertebral bodies, restoring lordosis, or for correcting a relativetranslation of the vertebral bodies. After insertion, guard 160 may be,but need not be, further fixated to the spine by the use of one or morefasteners including screws 196, 198, pins, or other suitable elements,preferably into each of the adjacent vertebral bodies. Again, it shouldbe noted that the presence of foot plate 174 is preferred when the guardis used anteriorly but is not essential.

[0072] With reference to FIGS. 11 and 12, the correct depth of the discspace to be prepared is determined. The correct disc space depth may bedetermined in a number of ways. For example, the depth may be determinedby pre-operative imaging studies such as plain radiographs, CAT scans,MRIs, and the like. Alternatively, the depth may be determined by directvisualization and/or measurement at the time of surgery, or byintraoperative radiographic monitoring, or any combination of the above.In using radiographic monitoring, for example, a lateral x-ray, thesurgeon can assess the depth of the disc space from the length of eitheror both of extensions 170, 172, and the remaining depth of the discspace. For example, alternatively the surgeon may radiographicallymonitor the progress of cutter mechanism 104 towards the posterioraspect of the vertebral bodies. Additionally, the surgeon by lookingtoward the spine through the passage of the guard can assess the bone tobe resected prior to resecting any bone. Intraoperative radiographicmonitoring will confirm to the surgeon whether the guard is generallyparallel to the disc space, the thickness of the bone to be cut, thedepth of resection for each of the adjacent vertebral bodies, if theguard is centered from side to side, and the depth of extensions intothe space so as to assess the depth of the disc space.

[0073] Disc penetrating extensions 170, 172 are inserted into the discspace to contact the adjacent end plates of the vertebral bodies and, ifnot already in the desired position, to position the adjacent vertebralbodies in the appropriate distraction and angular orientation to eachother for bone resection. After the adjacent vertebral bodies are in thedesired position, guard 160 may be secured to the spine such that footplate 174 is placed against the anterior aspect of the vertebral bodiesand screws 196, 198 are inserted through holes 176, 178 and into theadjacent vertebral bodies. The adjacent vertebral bodies are held in thedesired position relative to one another during the bone removalprocedure, and if desired, also during the spinal implant insertionprocedure.

[0074] Referring to FIG. 13, cutter mechanism 104 is advanced throughguard 160 into the disc space, removing bone from each of the adjacentvertebral bodies to the desired depth. It should be noted that theprogress of distal end 102 of the cutter instrument towards theposterior aspects of the vertebral bodies may be monitoredradiographically for greater accuracy. The desired depth also may bedetermined with adjustable depth stop 156 that may be set to limit thedepth of the cutter insertion. Cutter mechanism 104 is then removed.Debris can be removed by suction and/or irrigation, and optionally withgrasping instruments such as rongeurs.

[0075]FIG. 14 shows a cutaway side view of adjacent vertebral bodies V₁and V₂ that have had surfaces 184 and 186 formed in their respectiveadjacent end plates. The remaining portion of the more dense, bony rim188 assists in retaining the spinal implant in the desired positionbetween the adjacent vertebral bodies by acting as an abutmentpreventing lateral or posterior movement of the spinal implant. Theprepared faces of these abutment portions of the vertebral end platealso increase the surface area of contact between the spinal implant andthe vertebral body. FIG. 14 also shows the cut portion of the disc spacebeing taller than extension 172.

[0076] After removal of cutting mechanism 104, the surgeon has twooptions depending upon whether the cutter thickness and the spinalimplant height are similar or not. If the cutter thickness and spinalimplant height are not similar, then the surgeon may elect to removeguard 160 as shown in FIG. 15. Next, the correct spinal implant heightis determined. This determination may be made by knowing the extent ofdistraction prior to cutting, or by trialing the space with spacers todetermine the correct height, or by distracting the space and measuringthe height. Once the implant height has been determined, the correctspinal implant is selected which preferably has a width equal to thespace prepared and a length selected to correspond to the depth of thespace preparation or less, and a height sufficient to restoreappropriate spacing to the inter space. Additionally, the spinal implantis preferably selected to impart a desired amount of lordosis to thevertebral bodies adjacent the interspace.

[0077] The spinal implant is then inserted into the prepared space.During insertion, the prepared space may be held at least in partdistracted as the spinal implant is introduced into the prepared space.Preferably, the implant is introduced with an implant driver into thespine and advanced along the mid-longitudinal axis of the prepared spaceto the desired depth by urging it forward as by impaction, and/orpushing it forward, or the equivalent.

[0078] If, after removal of cutter mechanism 104, passageway 168 ofguard 160 has a height as great as the height of the implant to beinserted, then the surgeon may insert the spinal implant through guard160. It should be noted that if the guard was selected to have apassageway height greater than the cutter thickness, then the idealheight of the spinal implant may be determined by introducing into thedisc space progressively taller spacers to determine the optimal discspace distraction and implant height. After insertion of the implant,the implant driver, if one was used, is removed.

[0079] If the implant is to be inserted without the guard, then guard160 is removed from the adjacent vertebral bodies prior to the insertionof the implant.

[0080] Device 100 also may be used in a posterior approach, for example,between the adjacent vertebrae in the lower back, such as L₁ through S₁,from a posterior approach, or from posterior to the transverse processesof the vertebrae, including both straight posterior and posterolateral.If a posterior approach is used, many of the above steps apply. In orderto position guard 160, the dural sac is retracted towards the sideopposite of the insertion and protected along with the traversing nerveroot. For easier visualization of the area to be resected, guard 160 mayinclude inspection slots placed away from tissues such as the dural sacand nerves that need to be protected. Guard 160 is preferably placed toone side of the midline, that is, the line separating right and lefthalves of the vertebral bodies, especially when the surgeon intends toplace an implant on each side of the midline. During the posteriorapproach, the surgeon will normally prefer to place two implants, eachhaving a maximum width less than half of the width of the disc space andgenerally oriented from the back to the front of the disc space, orslightly toed in. Alternatively, the surgeon may elect to place but asingle implant. In such instance, the single implant may be placed morediagonally across the disc space allowing for the use of a longerimplant, or to place two implants from the same side.

[0081] In a posterior lateral approach, no laminar bone need be removedas the disc space is entered lateral to the spinal canal. In that case,two toed-in implants can be used or a single implant placed diagonallywhich may be longer than when the two are used. As the disc penetratingextensions themselves (the part in the disc) can be of various crosssectional shapes it may be preferred to utilize a distractor having aheight greater than its width so that it can be introduced on its sideand then rotated 90° to its height. In that case, it is preferred thatat least one of the diagonals, if not both, be reduced in length byreduction of the junctions or corners where the top and bottom meet thesides. Alternatively, the trial spacers may resemble the implant inshape, though it may be preferred to leave the bone engaging surfacessmooth to facilitate removing the trial implants or distractors. As usedherein, the term trials refers to spacers that are similar to an implantin shape but without a bone engaging surface such that it is smooth andlesser in height than an implant and used to determine the appropriatetension for the disc space in which a spinal implant is to be inserted.

[0082] FIGS. 16-18 illustrate various views of vertebral bodies withimplantation spaces that have been prepared by a device incorporatingthe present invention. The cross-hatching in these figures representsthe machined areas of vascular bone. FIG. 16 shows a top view of a firstvertebral body V₁ such as in the lumbar spine where the depth ofresection is sufficient to allow for the full diameter of the cutter topass into the disc space, leaving parallel straight sides and anatomiccontour at the trailing (anterior) aspect of the vertebral body. Thecreated space includes a leading portion adapted to correspond to theleading end of an implant and sides adapted to correspond to at least aportion of the sides of the implant. First vertebral body V₁ has asurface 190 formed by working end 110 as shown in FIG. 4. The width ofsurface 190 formed on first vertebral body V₁ closely matches the widthof working end 110 that was advanced into the disc space along a singlefront to back axis.

[0083]FIG. 17 shows the top view of a second vertebral body V₂ such asin the cervical spine where the depth of resection may be limited suchthat the full diameter of the cutter never passes into the bone. Thecreated space is adapted to correspond to at least a portion of theleading end of the implant and possibly a portion of the sides.

[0084]FIG. 18 shows the top view of a lumbar vertebral body V₃ showingside-by-side passes of the hemi-width cutter from a posterior toanterior approach. In such an instance, the cutter preferably has amaximum width of less than half the width of the disc space. Theprepared areas may or may not touch each other.

[0085] Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. An apparatus for preparing a space in the humanspine to receive an implant between adjacent vertebral bodies, saidapparatus comprising: a shaft having a proximal end and a distal endopposite said proximal end; a cutting mechanism proximate said distalend of said shaft, said cutting mechanism having a leading portionadapted for insertion into the spine and a trailing portion oppositesaid leading portion, said cutting mechanism having at least two cuttersadapted to remove bone from each of the adjacent vertebral bodies assaid cutting mechanism is moved to create an implantation space; a drivemechanism operably connected to said trailing portion of said cuttingmechanism for moving said cutters of said cutting mechanism; and a powersource operably connected to said drive mechanism.
 2. The apparatus ofclaim 1, wherein said cutters are adapted to simultaneously createpredetermined surface contours on the respective end plates of theadjacent vertebral bodies.
 3. The apparatus of claim 1, wherein saidcutters include teeth formed thereon to cooperatively engage said drivemechanism, said drive mechanism and said teeth being configured suchthat said cutters are rotated by said drive mechanism.
 4. The apparatusof claim 1, wherein a first and a second of said cutters are adapted tobe rotated in opposite directions by said drive mechanism.
 5. Theapparatus of claim 1, wherein said cutting mechanism has at least a topcutter and a bottom cutter.
 6. The apparatus of claim 1, wherein atleast a portion of said cutting mechanism is convex.
 7. The apparatus ofclaim 1, wherein at least a portion of said cutting mechanism is taperedoutwardly from a front surface of said leading portion.
 8. The apparatusof claim 1, wherein at least one of said cutters has a width, said widthsubstantially matches the width of the nucleus pulposus of a disc spacein which it is inserted.
 9. The apparatus of claim 1, wherein at leastone of said cutters is configured such that it is generally parallel tothe surface contour formed in the vertebral body as said cuttingmechanism is moved by said drive mechanism.
 10. The apparatus of claim1, wherein said cutting mechanism includes outwardly facing first andsecond cutters, and said first and second cutters are inclined relativeto one another.
 11. The apparatus of claim 1, wherein said cuttingmechanism is detachable from said mounting member.
 12. The apparatus ofclaim 1, wherein said cutting mechanism is driven in a reciprocating,arcuate motion by said drive mechanism.
 13. The apparatus of claim 1,wherein said cutting mechanism includes a wheel having cutter teethalong its perimeter.
 14. The apparatus of claim 1, wherein said drivemechanism is adapted to produce a rotary movement of said cuttingmechanism about an axis generally perpendicular to a longitudinal axisof said shaft.
 15. The apparatus of claim 1, wherein said drivemechanism is adapted to produce one of an oscillating rotation and avibratory motion of said cutting mechanism.
 16. The apparatus of claim1, wherein said drive mechanism comprises a gas-driven turbine poweredby a source of compressed gas.
 17. The apparatus of claim 1, whereinsaid drive mechanism is operable to move said cutting mechanism in atleast two degrees of freedom.
 18. The apparatus of claim 1, furthercomprising a suction mechanism for removing bits of debris created bysaid cutters of said cutting mechanism.
 19. The apparatus of claim 1,further comprising an irrigation channel configured through said shaftfor delivering irrigation fluid to the surgical site.
 20. The apparatusof claim 1, further comprising at least one stop member to limit thedepth of travel of said cutting mechanism into the spine.
 21. Theapparatus of claim 1, further comprising: a guide having an opening forproviding protected access to the adjacent vertebral bodies and a discspace therebetween, said opening being configured for passage of saidcutting mechanism through said guide.
 22. The apparatus of claim 1,further comprising: a guide having an opening for providing protectedaccess to the adjacent vertebral bodies and a disc space therebetween,said opening being configured for passage of said cutting mechanismthrough said guide; and first and second disc penetrating extensionsextending from said guide for insertion into the disc space between theadjacent vertebral bodies, each of said disc penetrating extensionshaving a portion for bearing against each of the adjacent end plates ofthe adjacent vertebral bodies, each of said portions of said discpenetrating extensions having an upper surface adapted to contact one ofthe adjacent end plates of the adjacent vertebral bodies and a lowersurface adapted to contact the other of the adjacent end plates of theadjacent vertebral bodies, said portions of said disc penetratingextensions having a height between said upper and lower surfaces and alength sufficient to properly align and distance apart the adjacentvertebral bodies.
 23. The apparatus of claim 22, wherein said upper andlower surfaces are parallel to each other along a substantial portion ofthe length of said portions.
 24. The apparatus of claim 22, wherein saidguide has an external surface at its distal end and said discpenetrating extensions are at least in part coextensive with saidexternal surface.
 25. The apparatus of claim 22, wherein said discpenetrating extensions are diametrically opposed to each other andspaced apart from one another to provide access to the adjacentvertebral bodies from within the disc space.
 26. The apparatus of claim22, wherein the height of said disc penetrating extensions have at leasta portion that approximates the height of a normal disc space betweenthe adjacent vertebral bodies.
 27. The apparatus of claim 22, whereinsaid disc penetrating extensions have a tapered leading end tofacilitate placement of said disc penetrating extensions into the discspace, said portion of said disc penetrating extensions having oppositesurfaces for bearing against the end plates of the adjacent vertebralbodies, said opposite surfaces diverging away from said guide along atleast a portion of their length.
 28. The apparatus of claim 22, whereinsaid upper and lower surfaces converge away from said guide along atleast a portion of their length.
 29. The apparatus of claim 22, whereinsaid disc penetrating extension has a length greater than one-half thedepth of the disc space measured from the anterior aspect to theposterior aspect of the disc space.
 30. The apparatus of claim 22,wherein said guide has an interior having a cooperating surface forguiding a corresponding cooperating surface on said cutting mechanism.31. The apparatus of claim 1, in combination with an implant sized andshaped to match the implantation space formed in the spine by saidcutting mechanism.
 32. The combination of claim 31, wherein said implantis one of a spinal implant and a spacer.
 33. The combination of claim31, further in combination with an implant driver configured tocooperatively engage said implant to insert said implant into the spine.34. The apparatus of claim 1, in combination with a distractor forspacing apart the adjacent vertebral bodies.
 35. The apparatus of claim1, wherein at least a portion of said cutters are separated by a spaceand substantially overlie one another, said drive mechanism beingconfigured to engage said cutters outside the space separating saidcutters.